Experimental time-domain evaluation and simulation of high power GaN HEMTS for RF Doherty Amplifier design

This paper presents an automatized, on-wafer time-domain active load-pull set-up developed for a Doherty-oriented characterization of High Power GaN High-Electron Mobility Transistors (HEMTs). From the on-wafer measured Time-Domain Waveforms (TDW) acquisition, all data required for the design of a Doherty Power Amplifier (DPA) are then directly extracted. With this measurement process, designers have then the direct knowledge of the optimal characteristics of high power transistors along the Output Back-Off (OBO). They also can deduce the maximum obtainable operating bandwidth of the final Doherty PA. Simultaneously to this measurement process, simulations based on the use of non-linear foundry electro-thermal model have also been performed to prove the validity of the method to predict Power Added Efficiency (PAE) performances versus OBO. Measurement and simulations have been applied to an 8×125μm AlGaN/GaN GH25 transistor from UMS foundry.